What is the purpose of the MyBatis dynamic tag?

The purpose of MyBatis dynamic tags is to dynamically generate SQL statements in XML mapping files. It offers a simple yet powerful way to create different SQL statements based on various conditions to meet different requirements.

Specifically, MyBatis offers the following dynamic tags:

1. : used to determine whether to include a certain SQL statement based on conditions. Regular comparison operators (such as equals, not equals, greater than, less than, etc.) can be used to evaluate the conditions.
2. , , and : used to implement logic similar to the switch statement in Java. The tag can contain multiple tags and one tag. When the condition of a tag is met, the corresponding SQL statement will be executed, otherwise the SQL statement inside the tag will be executed.
3. , , and : These tags are used to remove or add unnecessary spaces and symbols when generating SQL statements, as well as dynamically generating specific SQL fragments. Among them, the tag can be used to remove unwanted prefixes or suffixes, the tag is used to automatically add AND or OR keywords when generating the WHERE clause, the tag is used to generate the SET clause, and the tag is used to loop through collections or arrays.

These dynamic tags enable the dynamic generation of SQL statements based on different conditions in XML mapping files, thereby improving code flexibility and maintainability.